A beneficial response elicited by a heating of neoplastic tissue was reported by investigators in 1971. See the following publications in this regard:                (1) Muckle, et al., “The Selective Inhibitory Effect of Hyperthermia on the Metabolism and Growth of Malignant Cells” Brit J. of Cancer 25:771–778 (1971).        (2) Castagna, et al., “Studies on the Inhibition by Ethionine of Aminoazo Dye Carcinogenesis in Rat Liver.” Cancer Research 32:1960–1965 (1972).While deemed beneficial, applications of such thermotherapy initially were constrained to external surface heating. When external applications have been employed the resultant body structure heating has been described as having been uncontrolled in thermal localization resulting in temperature elevation of the whole body. Employment of diathermy has been reported with a resultant non-destructive inhibitory reaction. In general, no consensus by investigators as to the efficacy of thermotherapy with respect to tumor was present as late as the mid 1970s. See generally:        (3) Strom, et al., “The Biochemical Mechanism of Selective Heat Sensitivity of Cancer Cells—IV. Inhibition of RNA Synthesis.” Europ. J. Cancer 9:103–112 (1973).        (4) Ziet. fur Naturforschung 8, 6: 359.        (5) R. A. Holman, Letter “Hyperthermia and Cancer”, Lancet, pp. 1027–1029 (May 3, 1975).        
Notwithstanding a straightforward need for more effective techniques in the confinement of thermotherapy to localized internally located target tissue regions, investigators have established that tumor cells may be physiologically inhibited by elevating their temperatures above normal body temperature, for example, 37° C. for one major population, to a range exceeding about 40° C. The compromising but beneficial results further are predicated upon that quantum of thermal exposure achieved, based upon the time interval of controlled heat application. Thus, effective thermotherapies are characterized by an applied quantum of thermal energy established within a restrictive tissue periphery or volume of application with an accurately controlled temperature over an effective component of time.
One modality of thermotherapy is termed “hyperthermia” therapy, an approach to thermal treatment at temperatures elevated within somewhat narrow confines above normal body temperature. For instance, the elevation above a normal body temperature of 37° C. typically will fall within a range of 42° C. to 45° C. While higher temperature therapies have been described, hyperthermia therapy conventionally looks to affecting tissue to the beneficial effect of, for instance, negating neoplastic development, while avoiding denaturization, i.e., cell death or necrosis. It follows that an embracing of this therapeutic modality calls for the application of thermal control over specific tissue volumes.
Confinement of thermotherapy to a neoplasm-suspect target tissue volume internally disposed within the body without a generation of damage to healthy surrounding tissue has been considered problematic and thus the subject of diverse investigation. Experience in this field has revealed that achieving a controlled, thermo-therapeutic level of heat throughout a targeted tissue volume is difficult. In general, the distribution of induced heat across such tissue volumes can exhibit substantial variations. Vascularity and densities of heterogeneous tissues may impose such variations. For instance, the cooling properties of blood flow complicate the maintenance of a desired thermal dose at the target volume. A variety of approaches toward intra-body localized heat applications have evolved. Such efforts generally have been based upon the application of microwave energy (U.S. Pat. No. 4,138,998); the application of acoustic wave-based systems (ultrasound); the application of electric fields at RF frequencies (direct RF) from transmitting antenna arrays including an application subset utilizing inductive systems driven at relatively lower frequencies within the RF realm, and the utilization of infra red heaters.
Ultrasound is considered to be an acoustic wave above the normal range of human hearing, i.e., above about 20,000 Hertz. When employed clinically for thermo-therapeutic as well as diagnostic purposes, ultrasound system configurations perform in recognition of the acoustic impedance of investigated tissue. Acoustic impedance is the resistance to wave propagation through tissue, for example, due to absorbance, reflectance or molecularly induced scattering. Accordingly, the subject tissue volume will absorb some of the energy from the ultrasound waves propagated through it and the kinetic energy associated with the energy absorbed is converted into thermal energy to thus raise tissue temperature. See generally U.S. Pat. No. 6,451,044. When implementing ultrasound thermotherapy systems, careful control is called for to assure that minimum threshold tissue temperatures are reached and that maximum tissue temperature limits are not exceeded. Heretofore, temperature monitoring generally has been carried out by percutaneously injecting or otherwise inserting tethered temperature sensors such as thermocouples or thermistors into the targeted tissue region. Insertion of a tethered thermocouple may be accomplished by first inserting a hypodermic needle, then inserting a catheter through the needle with the sensor at its tip, whereupon the needle is withdrawn. Where hyperthermia therapy or heat induced immunotherapy are carried out, maintenance of relatively narrow temperature targets is sought, calling for a high level of control. For these thermotherapies, typically multiple therapy sessions are required, thus the generally undesirable injection or insertion of temperature sensors must be carried out for each of what may be many treatment sessions.
One approach has been advanced for ultrasound-based thermotherapy. In that approach, thermal localization is achieved by developing constructive wave interference with phased array-based wave guide applicators mounted to extend around the patient (see U.S. Pat. Nos. 5,251,645 and 4,798,215).
The microwave band generally is considered to extend from about 900 Mhz. Clinical studies have established that thermotherapy systems can be implemented with microwave radiating devices. Early endeavors utilizing microwave-based hyperthermia treatment evidenced difficulties in heating target tissue volumes at adequate depth while preventing surrounding superficial healthy tissue from incurring pain or damage due to hot spots exhibiting temperatures greater than about 44–45° C. However, later developments using adaptive phased array technology has indicated that relatively deeply located target tissues can be heated to thermotherapeutic temperatures without inducing the earlier difficulties. See generally the following publication:                (6) Fenn, et al, “An Adaptive Microwave Phased Array For Targeted Heating Of Deep Tumors In Intact Breast: Animal Studies Results” Int. J. Hyperthermia, Vol. 15, No. 1, pp 45–61 (1999).        
Inductively-based approaches to thermotherapy systems have received important attention by investigators. The coil transmitted outputs of these systems generally are focused for field convergence toward the target tissue volume and the resultant, internally thermally affected tissue region has been monitored in situ by thermo-responsive sensors such as rod-mounted thermocouples and thermistors. Those tethered heat sensors are inserted percutaneously into the target tissue region, being coupled by extra-body electrical leads extending to connections with temperature monitoring readouts. As before, the invasiveness of the monitoring electrical leads extending into the patients' body for this procedure has been considered undesirable. This particularly holds where repetitive but time-spaced procedures are called for, or the therapeutic modality is employed in thermally treating tumor within the brain.
The radio (RF) spectrum is defined as extending from the audio range to about 300,000 MHz. However direct RF thermotherapy has been described in conjunction with the 80 MHz to 110 MHz range.
Another approach is described as performing as a focused radio frequency/microwave region system, the election between these spectral regions being determined with respect to the depth of the target tissue. See: htp://www.bsdme.com/.
Efforts to regionalize or confine therapeutic tissue heating to predefined borders or volumetric peripheries have included procedures wherein small wire or iron-containing crystals (U.S. Pat. No. 4,323,056) are implanted strategically within the tissue region of interest. Implantation is achieved with an adapted syringe instrumentality. Electromagnetic fields then are introduced to the region to inductively heat the implanted radiative-responsive heater components and thus evoke a more regionally controlled form of thermotherapy. In one such approach, ferromagnetic thermoseeds have been employed which exhibit Curie temperature values somewhat falling within the desired temperature range for an elected thermotherapy. This achieves a form of self regulation by operation of the system about those Curie transitions. For instance, as radiative inductive excitation drives the thermoseeds to temperatures to within the permeability based state change levels associated with attainment of a Curie temperature range, the thermoseeds become immune to further application of external excitation energy. (See generally U.S. Pat. No. 5,429,583). Unfortunately, the Curie transition temperature range of the thermoseeds is relatively broad with respect to the desired or target temperature. This expanded Curie transition range is, in part, the result of the presence of the ferrite-based seeds within relatively strong electromagnetic fields. The result is a somewhat broad and poor regulation temperature band which may amount 10° or more. As a consequence, the auto-regulated devices are constrained to uses inducing tissue necrosis or ablation, as opposed to uses with temperatures controlled for hyperthermia therapies. See generally:                (7) Brezovich, et al., “Practical Aspects of Ferromagnetic Thermoseed Hyperthermia.” Radiologic Clinics of North America, 27: 589–682 (1989).        (8) Haider, et al., “Power Absorption in Ferromagnetic Implants from Radio Frequency Magnetic Fields and the Problem of Optimization.” IEEE Transactions On Microwave Theory And Techniques, 39: 1817–1827 (1991).        (9) Matsuki et al., “An Optimum Design Of A Soft Heating System For Local Hyperthermia” IEEE Transactions On Magnetics, 23(5): 2440–2442, (September 1987).        
Thermotherapeutic approaches designed to avoid the subcutaneous insertion of one or more temperature sensors have looked to the control of heating using modeling methodology. These approximating modeling methods are subject to substantial error due to differences or vagaries exhibited by the heterogeneous tissue of any given patient. Such differences may be due to variations in vascularity, as well as the gradual metamorphosis of a tumor mass. The latter aspect may involve somewhat pronounced variations in tissue physiologic characteristics such as density. See generally the following publication:                (10) Arkin, H. et al., “Recent Development In Modeling Heat Transfer in Blood Perfused Tissue.” IEEE Transactions on Bio-Medical Engineering, 41 (2): 97–107 (1994).        
Some aspects of thermotherapy have been employed as an adjunct to the use of chemotherapeutic agents in the treatment of tumor. Because of the precarious blood supply or vascularity and of the high interstitial fluid presence, such agents may not be effectively delivered to achieve a 100% cell necrosis. Further the tumor vessel wall may pose a barrier to such agents, and resultant non-specific delivery may lead to significant systemic toxicities. Studies have addressed these aspects of chemotherapy, for instance, by the utilization of liposomes to encapsulate the chemotherapeutic agents to achieve preferential delivery to the tumor. However the efficiencies of such delivery approaches have been somewhat modest. Clinically, hyperthermia therapy has been employed as a form of adjunct therapy to improve the efficiency of more conventional modalities such as radiation therapy and chemotherapy. For the latter applications the thermal aspect has been used to augment bloodstream borne release agents or liposome introduction to the tumor site. Hyperthermia approaches have been shown to trigger agent release from certain liposomes, making it possible to release liposome contents at a heated site (U.S. Pat. Nos. 5,490,840; 5,810,888). For any such thermotherapeutic application, an accurate temperature control at the situs of the release is mandated. See the following publications:                (11) Kong, et al., “Efficacy of Lipsomes and Hyperthermia in a Human Tumor Xenograft Model: Importance of Triggered Drug Release.” Cancer Research, 60: 6950–6957 (2000).        (12) Chung, J. E., et al., “Thermo-Responsive Drug Delivery From Polymeric Micelles Using Block Co-Polymers of Poly (N-isopropylacrylamide-b-butylmethacrylate) and Poly (butylmethacrylate), Journal of Controlled Release (Netherlands), 62(2): 115–127 (Nov. 1, 1999).        
Hyperthermia when used in conjunction with radiation treatment of malignant disease has been demonstrated as beneficial for destroying a specific tumor site. Clinical data has evolved demonstrating an improved efficacy associated with combined radiation and hyperthermia treatments as compared to radiation therapy alone. Such multimodal therapy concepts also have been extended to a combination of hyperthermia treatment with both radiation treatment and chemotherapy (radiochemotherapy). See generally:                (13) Falk et al., “Hyperthermia In Oncology” Int. J. Hyperthermia, 17: 1–18 (2001).        
Biological mechanisms at the levels of single cells activated by heat became the subject of scientific interest in the early 1960s as consequence of the apparently inadvertent temperature elevation of an incubator containing Drosophila melanogaster (fruit flies). These creatures, upon being heat shocked, showed the characteristic puffs indicative of transcriptional activity and discrete loci. See the following publication:                (14) Ritossa, “A New Puffing Pattern Induced By Temperature Shock and DNP in Drosophila.” Experientia, 18: 571–573 (1962).These heat shock loci encoding the heat shock proteins (HSPs), became models for the study of transcriptional regulation, stress response and evolution. The expression of HSPs may not only be induced by heat shock, but also by other mechanisms such as glucose deprivation and stress. Early recognized attributes of heat shock proteins resided in their reaction to physiologically support or reinvigorate heat damaged tissue. (See U.S. Pat. No. 5,197,940). Perforce, this would appear to militate against the basic function of thermotherapy when used to carry out the denaturization of neoplastic tissue. However, heat shock phenomena exhibit a beneficial attribute where the thermal aspects of their application can be adequately controlled. In this regard, evidence that HSPs, possess unique properties that permit their use in generating specific immune responses against cancers and infectious agents has been uncovered. Additionally, such properties have been subjects of investigation with respect to boney tissue repair, transplants and other therapies. See generally the following publications:        (15) Anderson et al., “Heat, Heat Shock, Heat Shock Protein and Death: A Central Link in Innate and Adoptive Immune Responses.” Immunology Letters, 74: 35–39 (2000).        (16) Srivastava, et al, “Heat Shock Proteins Come of Age: Primitive Functions Acquire New Role In an Adaptive World.” Immunity, 8(6): 657–665 (1998).        
Beneficial thermal compromization of target tissue volumes is not entirely associated with HSP based treatments for neoplastic tissue and other applications, for instance, having been studied in connection with certain aspects of angioplasty. Catheter-based angioplasty was first intentionally employed in 1964 for providing a transluminal dilation of a stenosis of an adductor hiatus with vascular disease. Balloon angioplasty of peripheral arteries followed with cautious approaches to its implementation to the dilation of stenotic segments of coronary arteries. By 1977 the first successful percutaneous transluminal coronary angioplasty (PTCA) was carried out. While, at the time, representing a highly promising approach to the treatment of angina pectoris, subsequent experience uncovered post-procedural complications. While PTCA had been observed to be effective in 90% or more of the subject procedures, acute reclosure, was observed to occur in approximately 5% of the patients. Stenosis was observed to occur in some patients within a period of a few weeks of the dilational procedure and restenosis was observed to occur in 15% to 43% of cases within six months of angioplasty. See generally:                (17) Kaplan, et al., “Healing After Arterial Dilatation with Radiofrequency Thermal and Non-Thermal Balloon Angioplasty Systems.” Journal of Investigative Surgery, 6: 33–52 (1993).        
In general, the remedy for immediate luminal collapse has been a resort to urgent or emergency coronary bypass graft surgery. Thus, the original procedural benefits attributed to PTCA were offset by the need to provide contemporaneous standby operating room facilities and surgical personnel. A variety of modalities have been introduced to avoid post PTCA collapse, including heated balloon-based therapy, (Kaplan, et al., supra) the most predominate being the placement of a stent extending intra-luminally across the dilational situs. Such stents currently are used in approximately 80% to 90% of all interventional cardiology procedures. While effective to maintain or stabilize intra-luminal dilation against the need for emergency bypass procedures, the stents are subject to the subsequent development of in-stent stenosis or restenosis (ISR). See generally:                (18) Holmes, Jr., “In-Stent Restenosis.” Reviews in Cardiovascular Medicine, 2: 115–119 (2001).Debulking of the stenotic buildup has been evaluated using laser technology; rotational atherectomy; directional coronary atherectomy; dualistic stent interaction (U.S. Pat. No. 6,165,209); repeated balloon implemented dilation, the application of catheter introduced heat to the stent region (U.S. Pat. No. 6,319,251); the catheter-borne delivery of soft x-rays to the treated segment, sonotherapy; light activation; local arterial wall alcohol injection; and ultrasound heating of a stent formed of an ultrasound absorptive material (U.S. Pat. No. 6,451,044).        
See additionally the following publications with respect to atherectomy for therapeutically confronting restenosis:                (19) Bowerman, et al., “Disruption of Coronary Stent During Artherectomy for Restenosis.” Catherization and Cardiovascular Diagnosis, 24: 248–251 (1991).        (20) Meyer, et al., “Stent Wire Cutting During Coronary Directional Atherectomy.” Clin. Cardiol., 16: 450–452 (1993).        
In each such approach, additional percutaneous intervention is called for. See generally the following publication:                (21) Vliestra and Holmes, Jr., Percutaneous Transluminal Coronary Angioplasty Philadelphia: F. A. Davis Co. (Mayo Foundation) (1987).        
Other approaches have been proposed including the application of electrical lead introduced electrical or RF applied energy to metallic stents, (U.S. Pat. No. 5,078,736); the incorporation of radioisotopes with the stents (U.S. Pat. Nos. 6,187,037; 6,192,095); and resort to drug releasing stents (U.S. Pat. No. 6,206,916 B1). While non-invasive control of ISR has been the subject of continued study, the development of a necessarily precise non-invasively derived control over it has remained an elusive goal.
Another application of hyperthermia is in orthopedics, as a means to stimulate bone growth and fracture healing. There are several FDA approved devices for stimulation of bone growth or healing, each with limitations and side effects. Therapies include invasive electrical stimulation, electromagnetic fields, and ultrasound stimulation. Decades old research has claimed a stimulation of bone growth by a mild increase in temperature of the boney tissue. Previous researchers have used such methods as inductive heating of implanted metal plates, or heating coils wrapped around the bone. The utility of these methods is limited by the invasive nature of the surgery needed to implant the heating elements and the inability to closely control tissue temperature. Moreover, therapeutic benefits have been inconsistent between different studies and experimental protocols. For a summary of past work, see generally:                (22) Wootton, R. Jennings, P., King-Underwood, C., and Wood, S. J., “The Effect of Intermittent local Heating on Fracture Healing in the Distal Tibia of the Rabbit.” International Orthopedics, 14: 189–193 (1990).        
A number of protocols have demonstrated a beneficial effect of hyperthermia on bone healing. Several studies indicate temperature affects bone growth and remodeling after injury. Hyperthermia may both improve blood supply and stimulate bone metabolism and have a direct effect on bone-forming cells by inducing heat shock proteins or other cellular proteins. In one experiment, rabbit femurs were injured by drilling and insertion of a catheter. Hyperthermia treatments were given at four-day intervals for 2–3 weeks using focused microwave radiation. Bones which had suffered an insult as a result of the experimental procedure showed a greater density of osteocytes and increased bone mass when treated with hyperthermia. Injured bones treated with hyperthermia showed completely ossified calluses after two weeks, while these processes normally take four weeks in untreated injuries. One problem with microwave heating of bone mass is the difficulty in predicting heat distribution patterns and maintaining the target tissue within the appropriate heat range.
When tissue is heated at too high of temperature, there can be irreversible cytotoxic effects which could damage bone and other tissues, including osteogenic cells, rather than induce healing. Certain studies have shown that induction of mild heat shock promotes bone growth, while more severe heat shock inhibits bone growth. Therefore, control and monitoring of the temperature of the targeted bone tissue is imperative to achieve therapeutic benefit and avoid tissue damage.
See additionally the following publications with respect to hyperthermia for therapeutically promoting osteogenesis:                (23) Leon, et al., “Effects of Hyperthermia on Bone. II. Heating of Bone in vivo and Stimulation of Bone Growth.” Int. J. Hyperthermia 9: 77–87 (1993).        (24) Shui et al., “Mild heat Shock Induces Proliferation, Alkaline Phosphatase Activity, and Mineralization in Human Bone Marrow Stromal Cells and Mg-63 Cells In Vitro.” Journal of Bone and Mineral Research 16: 731–741 (2001).        (25) Huang, C.-C., Chang, W. H., and Liu, H.-C. “Study on the Mechanism of Enhancing Callus Formation of Fracture by Ultrasonic Stimulation and Microwave Hyperthermia.” Biomed. Eng. Appl. Basis Comm. 10: 14–17 (1998).        
Existing protocols for therapeutically promoting osteogenesis are limited by the invasive nature and concomitant potential for infection for instance with tethered electrical stimulators; poor temperature control, and potential for tissue injury or reduced therapeutic benefit, for instance with microwave heating or other induced electromagnetic fields; difficulty in effectively applying therapy to the injured bone because of targeting difficulties or low patient compliance with prescribed repetitive therapy.
The host immune system can be activated against infectious disease by heat shock protein chaperoned peptides in a manner similar to the effect seen against metastatic tumors. Heat shock proteins chaperoning peptides derived from both viral and bacterial pathogens have been shown to be effective at creating immunity against the infectious agent. For infectious agents for which efficacious vaccines are not currently available (especially for intracellular pathogens e.g. viruses, Mycobacterium tuberculosis or Plasmodium) HSP chaperoned peptides may be useful for the development of novel vaccines. It is expected that purified HSP chaperoned peptides (e.g. gp96 complexes) used as vaccines for diseases caused by highly polymorphic infectious agents would be less effective against genetically distinct pathogen populations. For a summary of past work on HSP vaccines against infectious agents, see generally:                (26) Neiland, Thomas J. F., M. C. Agnes A. Tan, Monique Monnee-van Muijen, Frits Koning, Ada M. Kruisbeek, and Grada M. van Bleek, “Isolation of an immunodonminant viral peptide that is endogenously bound to stress protein gp96/GRP94.” Proc. Nat'l Acad. Sci. USA, 93: 6135–6139 (1996).        (27) Heikema, A., Agsteribbe, E., Wilschut, J., Huckriede, A., “Generation of heat shock protein-based vaccines by intracellular loading of gp96 with antigenic peptides.” Immunology Letters, 57: 69–74 (1997).        (28) Zugel, U., Sponaas, A. M., Neckermann, J., Schoel, B., and Kaufmann, S. H. E., “gp96-Peptide Vaccination of Mice Against Intracellular Bacteria.” Infection and Immunity, 69: 4164–4167 (2001).        (29) Zugel, U., and Kaufmann, S. H. E., “Role of Heat Shock Proteins in Protection from and Pathogenesis of Infectious Diseases.” Clinical Microbiology Reviews, 12: 19–39 (1999).        
In commonly owned co-pending application for U.S. patent Ser. No. 10/246,347, filed Sep. 18, 2002 and entitled “System, Method and Apparatus for Localized Heating of Tissue”, an approach to accurately carrying out an in situ elevation of the temperature of a target tissue volume is presented. Accuracy is achieved using untethered temperature sensor implants formed of ferromagnetic material which experiences an abrupt magnetic permeability state change within a very narrow temperature range. Temperature sensing is carried out by monitoring a very low level magnetic field extending through the position of the implant. For instance, the earth's magnetic field may be employed. Where inductively based heating is utilized, non-magnetic heaters may be implanted with the sensors and sensing is carried out intermittently in the absence of the inductably derived magnetic field.